The present invention relates to a pressurized fluid fixture support system for machine tool and other environments, and in particular to a power rotation apparatus wherein the workpiece fixture may be automatically rotated about one or more selected centers of rotation on the table.
The machining of large workpieces often involves very difficult positioning and repositioning of the workpiece when the various portions thereof are machined. In many cases, it is necessary to use hoists for elevating and moving the workpiece both to and from the machine tool table, and on the table itself where repositioning is necessary for sequential machining steps.
In order to overcome these problems, an air-float system, wherein the workpiece is mounted to a fixture which in turn is supported on a film of pressurized air, has been developed. This system is described in detail in U.S. Pat. No. 4,058,885 in the name of Raymond A. Bergman, which patent is incorporated herein by reference. In the system, a table is provided with fluid passages and a plurality of fluid outlets distributed over the surface of the table so that a cushion of pressurized air may be provided underneath the workpiece fixture. By virtue of the fluid pressure film, substantially friction-free movement of the fixture on the table is possible thereby permitting positioning and repositioning to be accomplished by a single operator without the need for hoisting equipment.
In order for the fixture to be rotated and translated from one position to another, the table may be provided with one or more retractable pivot pins which project upwardly from the table surface. The pins may either be receivable in a socket in the bottom of the fixture, in which case the fixture is constrained to move circularly on the table as it is manually turned, or, alternatively, they may be received in one or more slots so that the fixture is not only rotatable but also translatable. Cooperating pairs of retractable pin and socket locating devices on the fixture and table provide for accurate location of the fixture in a variety of predetermined positions. Clamps may also be provided for clamping the fixture in the located positions during machining. The clamps may be of the conventional T-slot type, the bayonet type as described in U.S. patent application Ser. No. 829,358 filed Aug. 31, 1977 in the name of Raymond A. Bergman, or of the automatic retracting T-clamp type disclosed in copending U.S. patent application Ser. No. 40,072 filed May 17, 1979.
The table may be provided with a dual centering pin feature, as disclosed in U.S. Pat. No. 4,143,868, if additional flexibility is desired in positioning and locating the fixture. The dual centering pin comprises an outer pin which is engagable with the fixture slots, and an inner pin received within the outer pin with means for causing the inner pin to extend upwardly out of the outer pin so as to engage holes in the slots. When the inner pin is retracted, the workpiece fixture is translatable on the table in engagment with the outer pin, and when the inner pin is extended and received within one of the fixture holes within the slots, the fixture may be rotated about it to the desired position.
It is often desirable to machine more than one side of a workpiece with a single setup, for example, when drilling bolt holes. This is especially desirable in the case where the part may have many sides, such as octagonal parts, and wherein the machining operation is the same for each side.
An apparatus commonly used for this purpose is a rotary table, wherein the top plate is rotated about a single center axis in front of the machine tool or tools. Thus, each side of the workpiece is presented to the tool in sequential fashion as the table surface is rotated. Such an apparatus is also useful for machining relatively small parts in high production environments. In this case, two or more parts are mounted to the table in back-to-back fashion, and machined in turn. A rotary table also finds use in machining operations where a plurality of different machining functions are performed sequentially, as by different machine tools placed around the perimeter of the rotary table and machining the part simultaneously or sequentially.
Although a rotary table is very useful for certain selected operations, such as those discussed above, it lacks versatility in that it is not suitable for a great many machining operations wherein the part size is not compatible with the table size, or where only one machining operation is to be performed on the part at that station. Furthermore, typical rotary tables are expensive and quite large in size, thereby making them unattractive except for certain selected machining operations.
Thus, there exists a great need for a machine tool table which is relatively modest in cost and of a small size, yet possessing many of the advantages of rotary tables, such as the ability to rapidly and efficiently machine multi-sided parts. Also, since numerical control machining installations are becoming more and more common, such a table should be compatible with an automatic control environment.